1. Field of the Invention
The present invention relates generally to telecommunications devices and more particularly to the use of modems in DSL and analog environments.
2. Background Information
Standard analog modems (modulator-demodulator devices) are currently commonplace in the home and office environments, where they are used to enable electronic devices, such as personal computers, to transmit data over existing telephone lines (made of small gauge copper wire) to other electronic devices. Data is stored digitally in such devices, but is converted by an analog modem to be transmitted over the lines in analog form. A data stream is established between a sender (i.e., originating electronic device) and a receiver (i.e., receiving electronic device) by using the resources of an entire telecommunications system. In other words, data is transmitted from the sender's local loop, through a telephone switching system, and to the receiver's local loop. Because the lines used by analog modems to transmit data only use a frequency range of about 0-3400 Hz, a data transmittance limit of about 56,000 bits-per-second (bps) exists for communication through the lines. An analog modem operating at this high end may, for example, be a modem operating under the ITU V.90 standard.
An emerging technology called Digital Subscriber Line (DSL) offers users data transmittance speeds much higher than those offered by standard modem systems. Unlike the switching systems associated with analog communications, modems that support DSL must be physically connected at one end of a telephone line (i.e., copper wire) to a phone company central office at the other end of the line, which is typically no longer than 18,000 feet. However, by using a much greater bandwidth (from 60 KHz to 1 MHz), DSL allows higher transfer rates, but is limited to 18,000 feet in reach. Currently, DSL modems are capable of transmitting data from around 8.128 Mbps to 512 Kbps (downstream) and 128 Kbps to 800 Kbps (upstream).
In addition, because DSL technology uses a different area of the spectrum than regular telephony, it is possible to have simultaneous voice and data use of a single copper connection. One example of communications technology that provides this is called Asymmetric DSL (ADSL). In other words, the “lower” range of frequencies (i.e., up to 3400 Hz) is used for the transmittance of voice data, while the “higher” range is used by a DSL modem to transmit digital data. In this way, a DSL connection is always “on” and separate from any voice data transmissions. However, many phones may pass onto the copper frequencies higher than 3400 kHz and allow voice data to interfere with a DSL data stream. Conversely, the higher frequencies used by a DSL modem may be picked up by a phone, which will cause static in the voice data stream.
Two methods currently exist for countering these problems. The first one creates a “splittered” environment, where devices called “splitters” are attached to phone lines in close proximity to the home or office where data is to be received. As shown in the FIG. 2 example, a mixed-signal S(1) is received by a splitter 205 from center 201, which may be, for example, a phone company central office. The mixed-signal S(1) includes both analog and DSL data and is spectrally separated by splitter 205 into analog signal S(2) and DSL signal S(3). Phone 202 receives analog signal S(2) through wall jack 206 and DSL modem 203 receives DSL signal S(3) through wall jack 207. Data from DSL signal S(3) is then processed and sent by DSL modem 203 to a processor 204, where information may be presented to a user (e.g., via an Internet browser). Splitter 205 also acts as a low pass filter, allowing only voice data frequencies (i.e., 0-3400 Hz) to be transmitted to and from the phone, thereby eliminating any interference between a phone and a DSL modem.
The second method creates a “splitterless” environment, where lower frequency data (i.e., analog voice) is not separated or “split” from the higher frequency data (i.e., digital DSL) before being received from a wall jack. As shown in the FIG. 3 example, center 301 transmits a mixed-signal S(4), which is received by microfilter 305 and DSL/analog combo modem 303 through wall jacks 306 and 307, respectively. In such an environment, the installation of a separate splitter (e.g., splitter 205 in FIG. 2) is avoided. Combo modem 303 is a modem which is capable of supporting both DSL and analog transmission and can also provide an internal splitting function. Thus, processor 304 is able to receive both digital data and converted analog data from combo modem 303. Microfilter 305 is a type of device currently used in splitterless environments to eliminate interference between voice and data frequencies. Such devices are essentially customer-installable low-pass filters connected between phones and wall jacks with the use of two RJ-11 (Registered Jack-11) jacks. In this example, phone 302 only receives data at a frequency of about 3400 Hz or lower, that is, data not filtered out by microfilter 305.
Currently available DSL/analog combo modems are equipped with two RJ-11 jacks for connection to outlets. In the interest of cost and space reduction, however, it would be preferable to have such a combo modem with only a single RJ-11 jack. An example of such a modem is described in co-pending U.S. patent application Ser. No. 09/792,946, the disclosure of which is hereby incorporated by reference in its entirety. In a splitterless environment, where both analog data and digital data frequencies are carried on a single line, a combo modem with only one RJ-11 jack is immediately useful. However, in a splittered environment, analog and digital frequencies arrive at separate wall jacks or outlets. When using a DSL/analog combo modem with one RJ-11 jack, a user is able to transmit and receive only one of the frequencies at a single time. In other words, a user with a one-jack combo modem connected to a wall jack receiving analog frequencies (i.e., voice) must disconnect the modem from the wall jack and connect it to a wall jack receiving digital frequencies (i.e., DSL) if the user desires to use the DSL capability of the modem.